One cause of epilepsy is mutations in proteins that function in the brain. Fukata et al. identified the partners of a complex of proteins located at rat brain synapses. Of the various components, one (LGI1) seems to function as a ligand, one (ADAM22) as a receptor, and one (PSD-95) as a scaffolding anchor. LGI1 controls the strength of excitatory synapses. Both the ligand and the receptor of this complex are implicated by genetics and mutations as causing certain types of epilepsy.